Beside my PC, all the devices showed a ~ 5MB/s download stream while my PC showed things like 0.1MB/s <> 0.8MB/s.
If I disconnected the WiFi connection and than reconnected - the speed test showed a 5MB/s download speed for few tests, but after a minute or so - the connection dropped down to the under 1Mb/s limit.

Doing the same tests on my PC using windows 7 showed no such problems and the connection was steady at 5MB/s.

I've searched around askubuntu and tried several things (turned off ipv6 and power management ) but with no success.